Re: streaked windows and lights

[Leigh Palmer <palmer@SFU.CA>]

> I made a mess of my windshield this morning when the fluid was frozen and
> the wipers made a streaked smear before my very eyes. Oncoming cars and
> taillights ahead created a wonderful pattern of elongated "rays" that ran
> to the center of the arc. I tried to explain this phenomenon to myself but
> was never satisfied with my answer. I was thinking some kind of
> diffraction effect but can not put all together. So..Can anyone help me
> out? Please.

You made a number of concentric positive cylindrical lenses on your
windshield. A cylindrical lens minifies the scene seen through it.
Thus you saw an image of a taillight in every cylindrical lens at
once. Diffraction could also do this, but I suspect the geometrical
optical contribution is more important.

Leigh